Science in the Making: Right Hand, Left Hand. III: Estimating historical rates of left-handedness

Abstract

The BBC television programme Right Hand, Left Hand, broadcast in August 1953, used a postal questionnaire to ask viewers about their handedness. Respondents were born between 1864 and 1948, and in principle therefore the study provides information on rates of left-handedness in those born in the nineteenth century, a group for which few data are otherwise available. A total of 6,549 responses were received, with an overall rate of left-handedness of 15.2%, which is substantially above that expected for a cohort born in the nineteenth and early twentieth centuries. Left-handers are likely to respond preferentially to surveys about handedness, and the extent of over-response can be estimated in modern control data obtained from a handedness website, from the 1953 BBC data, and from Crichton-Browne's 1907 survey, in which there was also a response bias. Response bias appears to have been growing, being relatively greater in the most modern studies. In the 1953 data there is also evidence that left-handers were more common among later rather than early responders, suggesting that left-handers may have been specifically recruited into the study, perhaps by other left-handers who had responded earlier. In the present study the estimated rate of bias was used to correct the nineteenth-century BBC data, which was then combined with other available data as a mixture of two constrained Weibull functions, to obtain an overall estimate of handedness rates in the nineteenth century. The best estimates are that left-handedness was at its nadir of about 3% for those born between about 1880 and 1900. Extrapolating backwards, the rate of left-handedness in the eighteenth century was probably about 10%, with the decline beginning in about 1780, and reaching around 7% in about 1830, although inevitably there are many uncertainties in those estimates. What does seem indisputable is that rates of left-handedness fell during most of the nineteenth century, only subsequently to rise in the twentieth century.

Keywords:

• Handedness
• Rate
• Historical
• Nineteenth century
• Response bias

Acknowledgements

We are extremely grateful to Dr Chuck Wysocki for providing the raw data from the Gilbert and Wysocki study.

Notes

¹It should be noted that the loess curve is only a first approximation to the best-fitting line because both (a) no weighting is applied according to the size of the various data sets, and (b) it is a theory-free description of the data, unlike the Weibull function.

²The regression equation described below would predict that there should be about 4.65× as many left-handers found compared with the general population, whereas there were actually 10.44×, about 2.2× as many as expected above the normal excess of left-handers. We suspect that some parents either encouraged their left-handed children to respond or perhaps even responded on their behalf.